This Invention Relates To High Strength Thin Gauge Steel Sheet And Method of Production thereof. BACKGROUND ART Recently, due to the need for reducing the weight of automobiles and improving collision safety, high strength steel sheet excellent in formability into chassis frame members and reinforcement members, seat frame parts, and the like are being strongly demanded. From the aesthetic design and chassis design requirements, complicated shapes are sometimes demanded. High strength steel sheet having superior working performance is therefore necessary. On the other hand, due to the increasingly higher strength of steel sheet, the working method is frequently shifting from the conventional drawing using wrinkle elimination to simple stamping and bending. Especially, when the bending ridge is an arc or other curve, stretch flanging where the end face of the steel sheet is elongated is sometimes used. Further, there are also quite a few parts which are worked by burring to expand a worked hole (preparatory hole) to form a flange. The amount of the expansion in the large case is, up to 1.6 times the diameter of the preparatory hole. On the other hand, the phenomenon of springback or other elastic recovery after working a part occurs more readily the higher the strength of the steel sheet and obstructs securing the precision of the part. In this way, these working methods require stretch flangeability, hole expandability, bendability, and other local formability of the steel sheet, but conventional high strength steel sheet do not have sufficient performance, cracks and other defects occur, and stable working of the products is not possible. Therefore, up to now, high strength steel sheet improved in stretch flangeability has been proposed in Japanese Patent Publication (A) No. 9-67645, but there has been a remarkable increase in the need for improvement in workability, in particular hole expandability and therefore further improvement enabling simultaneous improvement in elongation as well. DISCLOSURE OF INVENTION The present invention has as its object to solve the problems of the prior art as explained above and realize high strength thin-gauge steel sheet with excellent elongation and hole expandability and a method of production for the same on an industrial scale. Specifically, it has as its object to realize high strength thin-gauge steel sheet exhibiting the above performance by a tensile strength of 500 MPa or more and a method of production of the same on an industrial scale. The inventors studied the methods of production of high strength thin-gauge steel sheet with excellent elongation and hole expandability and as a result discovered that to further improve the ductility and hole expandability of steel sheet, in the case of high strength cold rolled steel sheet with a tensile strength of steel sheet of 500 MPa or more, the form and balance of the metal structure of the steel sheet and the use of tempered martensite are important. Furthermore, they discovered steel sheet establishing a specific relationship between the tensile strength and Si and Al so as to secure a suitable ferrite area fraction and avoid deterioration of the chemical conversion ability and plating adhesion and controlling precipitates and other inclusions contained inside by the addition of Mg, REM, and Ca so as to improve the local formability and thereby improve the press formability to an unparalleled level and a method of production of the same. (1) High strength thin-gauge steel sheet with excellent elongation and hole expandability characterized by being comprised of, by mass%, C: 0.03 to 0.25%, Si: 0.4 to 2.0%, Mn: 0.8 to 3.1%, P<0.02%, S<0.02%, Al<2.0%, N<0.01%, and a balance of Fe and unavoidable impurities and having a microstructure comprised of ferrite with an area fraction of 10 to 85% and residual austenite with a volume fraction of I to 10%, an area fraction of 10% to 60% of tempered martensite, and a balance of bainite. (2) High strength thin-gauge steel sheet with excellent elongation and hole expandability according to (1) characterized by further including as chemical ingredients one or more of V: 0.005 to 1%, Ti: 0.002 to 1%, Nb: 0.002 to 1%, Cr: 0.005 to 2%, Mo: 0.005 to 1%, B: 0.0002 to 0.1%, Mg: 0.0005 to 0.01%, REM: 0.0005 to 0.01%, and Ca: 0.0005 to 0.01%. (3) High strength thin-gauge steel sheet with excellent elongation and hole expandability according to (1) or (2) characterized by further satisfying the following formula (A): (0.0012x[TS target value]-0.29)/3<[Al]+0.7[Si]<1.0 (A) TS target value is design value of strength of steel sheet in units of MPa, [Al] is mass% of Al, and [Si] is mass% of Si, (4) A method of production of high strength thin- gauge steel sheet with excellent elongation and hole expandability characterized by producing a slab comprised of, by mass%, C: 0.03 to 0.25%, Si: 0.4 to 2.0%, Mn: 0.8 to 3.1%, P<0.02%, S<0.02%, Al<2.0%, and N<0.01% and, further, when necessary, one or more types of V: 0.005 to 1%, Ti: 0.002 to 1%, Nb: 0.002 to 1%, Cr: 0.005 to 2%, Mo: 0.005 to 1%, B: 0.0002 to 0.1%, Mg: 0.0005 to 0.01%, REM: 0.0005 to 0.01%, and Ca: 0.0005 to 0.01%, and a balance of Fe and unavoidable impurities, heating it in a range of 1150 to 1250°C, then hot rolling it in a temperature range of 800 to 950°C, coiling it at 700°C or less, then pickling it as normal, then cold rolling by a reduction rate of 30 to 80%, then, in a continuous annealing process, soaking it at 600°C to the Aca point+50°C for recrystallization annealing, cooling to 600°C to the Ar3 point by an average cooling rate of 30°C/s or less, then cooling to 400°C or less by an I average cooling rate of 10 to 150°C/s, then holding at higher than a cooling end temperature of said cooling and 150 to 400°C for 1 to 20 minutes, then cooling to thereby obtain a metal structure having a microstructure comprised of ferrite with an area fraction of 10 to 85% and residual austenite with a volume fraction of 1 to 10%, an area fraction of 10% to 60% of tempered martensite, and a balance of bainite. (5) A method of production of high strength thin- gauge steel sheet with excellent elongation and hole expandability according to (4) characterized by, in the continuous annealing process, soaking at 600°C to the Ac3 point+50°C for recrystallization annealing, cooling by an average cooling rate of 10 to 150°C/s to 400°C or less, then heating and holding a first time at 150 to 400°C for I to 20 minutes, then heating and holding a second time at a temperature 30 to 300°C higher than the first heating and holding temperature to 500°C for 1 to 100 seconds, then cooling. (6) A method of production of high strength thin- gauge steel sheet with excellent elongation and hole expandability according to (4) characterized by, in the continuous annealing process, soaking at 600°C to the AC3 point+50°C for recrystallization annealing, cooling by an average cooling rate of 10 to 150°C/s to 400°C or less, then heating and holding a first time at 150 to 400°C for 1 to 20 minutes, cooling to the martensitic transformation point or less, heating and holding a second time at the cooling end temperature to 500°C for 1 to 100 seconds, then cooling. BEST MODE FOR CARRYING OUT THE INVENTION The biggest characteristic of the structure of a high strength thin-gauge steel sheet according to the present invention is that by performing the necessary heat treatment after an annealing and quenching process, a metal structure containing ferrite, residual austenite, tempered martensite, and bainite in a good balance can be obtained and a material having extremely stable ductility and hole expandability can be obtained. Next, the limitations of the chemical ingredients of the present invention will be explained. C is an important element for improving the strengthening and hardenability of the steel and is essential for obtaining a composite structure comprised of ferrite, martensite, bainite, etc. To obtain the bainite or tempered martensite advantageous for obtaining TS>500 MPa and local formability, 0.03% or more is necessary. On the other hand, if the content becomes greater, the cementite or other iron-based carbides easily become coarser, the local formability deteriorates, and the hardness after welding remarkably rises, so 0.25% was made the upper limit. Si is an element preferable for raising the strength without lowering the workability of the steel. However, if less than 0.4%, a pearlite structure harmful to the hole expandability is easily formed and, due to the drop in the solution strengthening of the ferrite, the hardness difference between the formed structures becomes greater and deterioration of the hole expandability is invited, so 0.4% was made the lower limit. If over 2.0%, due to the rise in the solution strengthening of ferrite, the cold reliability drops and the Si oxides formed at the steel sheet surface cause a drop in the chemical conversion ability. Further, the plating adhesion and weldability also drop, so 2.0% was made the upper limit. Mn is an element which has to be added from the viewpoint of securing the strength and, further, delaying the formation of carbides and is an element effective for formation of ferrite. If less than 0.8%, the strength is not satisfactory. Further, formation of ferrite becomes insufficient and the ductility deteriorates. If over 3.1%, the martensite becomes excessive, a rise in strength is invited, and the workability deteriorates, so 3.1% was made the upper limit. P, if over 0.02%, results in remarkable solidification segregation of the time of casting, invites internal cracking and deterioration of the hole expandability, and causes embrittlenient of the weld zone, so 0.02% was made the upper limit. S is a harmful element since it remains as MnS and other sulfide-based inclusions. In particular, the higher the matrix strength, the more remarkable the effect. If the tensile strength is 500 Mpa or more, it should be suppressed to 0.02% or less. However, if Ti is added, precipitation as a Ti-based sulfide occurs, so this restriction is eased somewhat. Al is an element required for deoxidization of steel, but if over 2.0% increases the alumina and other inclusions and impairs the workability, so 2.0% was made the upper limit. To improve the ductility, addition of 0.2% or more is preferable. N, if over 0.01%, degrades the aging behavior and workability of the matrix, so 0.01% was made the upper limit. To obtain high strength steel sheet, generally large amounts of additive elements are necessary and formation of ferrite is restrained. For this reason, the ferrite fraction of the structure is reduced and the fraction of the second phase increases, so especially at 500 MPa or more, the elongation falls. For improvement of this, normally addition of Si and reduction of Mn are frequently used, but the former degrades the chemical conversion ability and plating adhesion, while the latter makes securing the strength difficult, so these cannot be utilized in the steel sheet intended by the present invention. Therefore, the inventors engaged in in-depth studies and as a result discovered the effects of Al and Si. They discovered that when there is a balance of Al, Si, and TS satisfying the relationship of formula (A), a sufficient ferrite fraction can be secured and excellent elongation can be secured. (0.0012x[TS target value]-0.29)/3<[Al]+0.7[Si]